Amplifying circuit for ultra-short waves



March 2, 1943.

A. VAN DER ZIEL ETAL AMPLIFYING CIRCUIT FOR ULTRA SHORT WAVES Filed May 9, 1941 Fly 2 4 INVENTORS ALDERT VAN DER Z/EL MAX/MILIAAN J- 0. STRUT T KNOL BY KOR ATTORNEY Patented Mar. 2, 1943 AMPLIFYIING omourr FOR ULTRA-SHORT waves Aldert van der Ziel, Maxi'miliaan *ruuus Otto Strutt, and Kornelis Swier Knoi, Eindhoven, Netherlands; vested-in the Alien Property Custodian Application May 9, 1941, Serial nasaacsc In the Netherlands June 19, 19%

I 9 Claims.

Inv the mpending application, Serial No. 340,514, filed June 14, 1940, there has been described an amplifying-circuit arrangement for ultra-short waves in which use is made of a pushpull arrangement of two amplifying systemseach comprising at least one cathode, one control-grid, one screen-grid and an anode and in which the cathodes of the two systems are interconnected through as short a lead as possible,

each of the screen-grids being connected for high-frequencies to the corresponding cathode through an inductance of such a size that the input-damping of the circuit is zero or negative.

For a clear understanding of the invention reference willbe had to the several figures of the accompanying drawing in which Fig. 1 is a circuit of the above prior application and over which the present invention-is an improvement, and Figs. 2 to 4 are various circuits which embody the invention.

Referring first to the circuit arrangement of from a dipole antenna is supplied to the terminals I and 2 and inductively transmitted to the input-oscillatory circuit 3. The ends of the oscillatory circuit 3 are connected in push-pull arrangement to the control-grids of the push-pull amplifying tube 4. This tube comprises two am plifying systems each consisting of a cathode, a control-grid, a screen-grid, a suppressor grid connected to the cathode and an anode. Between the anodes is interposed the output-oscillatory circuit 5 from which the amplified voltage can be taken at the terminals 6 and I.

The cathodes ofthe amplifying systems are interconnected through as short a lead as pos sible. The screen-grids are each separately led out of the tube and connected for high frequencies to the cathode through inductances 8 and 9. These inductances are so proportioned that the input-damping of tube 4 is zero or negative so that the circuit 3 -is not damped or even undamped by the tube. The value of the self-induction of coils 8 and 9 required therefor is of the order of magnitude of 10- henries.

The circuit-arrangement set out above has the drawback that the ratio between the signal current and the noise-current in the anode circuit is very unfavourable.

According to the'invention this drawback is obviated by connecting the anode of each of the amplifying systems through the corresponding part of the output-impedance for high frequencies either to the end, facing the screen grid, of the inductance inserted in the corresponding Fig. 1, the input-voltage originating, for instance,

' Hence this current will substantially be in phase screen-grid circuit, in other words, the screen grid end of the inductance, or to a point of this inductance located between the ends, that is, an intermediate point. v

The invention is based on the recognition that the unfavorable signal-noise ratio in the circuit disclosed in the principal application is due to over-compensation of the distribution noise, which may be explained as follows by reference to Fig. 1. r

The distribution noise results from variations in the current-distribution between the anode and the screen-grid. In this case a random increase of the anode-current involves an equal decrease of the screen-grid current so that the distribution noise-current in the anode circuit and the screen-grid circuit are in phase opposition with respect to one another. When the screen-grid circuit includes an inductance, for instance the inductance 8 shown in Fig. 1, the distribution noise-current will set up a noise-voltage across this inductance which voltage leads in phase by with respect to the distributionnoise current flowing in the screen-grid circuit and which consequently lags by 90 relatively to the distribution-noise currentflowing in the anode-circuit. This voltage evolves a current through the center of the input-impedance 3 connected to the cathodes, the part of the inputimpedance located between this center of the control-grid of the amplifying system in question, and the control-grid screen-grid capacity designated by It in the drawing, whose phase is mainly determined by the control-grid/screen-grid capacity and which consequently leads in'phase by about 90 relatively to the said noise-voltage.

with the distribution noise current flowing in the anode-circuit and setup a voltage across the part of the input-circuit 3 located between the center and the control-grid, which voltage is also in phase with the distribution noise-current flowing in the anode-circuit. It is to be remarked that only those frequencies of the distribution-noise spectrum are of importance which are transmitted by thecircuit and to which consequently the circuit 3 practically constitutes an ohmic resistance. Frequencies towards which the, circuit 3 no longer behaves as an ohmic resistance and which thus might give rise to voltages of another phase between the center and the control-grid may be left out of consideration.

For thefrequencies of the distribution noise spectrum transmittewby the circuit there will be set up, a-voltage at the control grid. as appears from what has been said above, which is correlated with the distribution noise and in phaseopposition with the distribution noise current flowing in the anode-circuit and which consequently contributes to the anode-current which is also in phase-opposition with the distribution noise current in the anode current. Thus the distribution noise in the anode circuit might be entirely avoided by giving the inductance 8 suitable proportions.

If, however, the inductances 8 and 9 are so proportioned that the input-damping is zero or negative the values of these inductances are much higher than were necessary for compensation of the distribution. noise. Hence the distribution noise is far over-compensated and the circuit is liable to more'noise than were the case in the absence of the inductances 8 and 9.

The distribution noise-current in the anode circuit and the screen-grid circuit being in phase opposite will cancel out each other in that part of the connection between screen-grid and cathance of the part extending within the tube is smaller than is necessary for compensation of the distribution noise, in which case complete removal of the distribution noise can be achieved by means of the circuit represented in Fig. 4.

In the circuit shown in Fig. 4 the anodes are connected through circuits 5' and 5" respectively to tappings of the inductances 8 and 9. In this ode which is common to the screen-grid circuit and the anode-circuit. So there does not flow distribution noise-current in this part of the screen-grid circuit. Now the invention consists in that over-compensation of the distribution noise is avoided by inserting at least a part of the inductance required for removing the inputdamping in this common part of the anode-circuit and the screen-grid circuit.

The invention will now be more fully explained by reference to Figures 2 to 4.

The circuit represented in Fig. 2 differs from that shown in Fig. 1 in that the output-impedance 5 is split up into two parts 5' and 5", the

anode of the upper amplifying system being connected through the circuit fi' to the end, facing the screen grid, of the inductance 8 inserted in the corresponding screen-grid circuit, and the anode of the bottom amplifying system being connected through the circuit 5" to that end of the inductance 9 which faces the screen-grid. The distribution noise-current now flows in the two amplifying systems from the anode through the circuit 5', 5" respectively to the screen-grid and does not pass through the inductance B, 9 respectively so that over-compensation of the distribution noise can no longer occur. In this case the inductances 8 and 9 are traversed not only by the signal current of the screen-grid, but also by that of the anode. As a result of this the coils 8 and 9 for removing the input-damping may have a much lower self-induction than in the circuit shown in Fig. 1.

In amplifying very short waves the distribution noise-current may sometimes involve a high noise voltage across the inductance of the part of the supply lead of the screen-grid extending inside the tube so as to cause over-compensation of the distribution noise. In this case it is-advantageous to make use of the circuit shown in Fig. 3 in which the screen-grids are each furnished with two separated supply leads. In this arrangement each screen-grid is connected through one of the said supply leads and the circuit 5', 5" respectively to the corresponding anode, and through the other supply lead and the inductance 8, 9 respectively to the cathode. In this case there is no coupling at all between the circuit traversed by the distribution noisecurrent and the screen-grid cathode circuit so that over compensation of the distribution noise is entirely obviated.

On the other hand it may be that the inductcase the self induction of part 8', 9 respectively which is located between the tapping and the screen-grid and consequently traversed by the distribution noise-current is chosen so as exactly to compensate the distribution noise. Furthermore the part 8", 9" respectively between the tapping and the cathode is so chosen that under the joint action of parts 8', 8" and 9', 9". respectively the desired undamping of the input-circuit is obtained.

The same effect can be obtained in the circuit shown in Fig. 3 by providing that a part of the two supply leads of each screen-grid coincides within the tube.

What we claim is:

1. An amplifying-circuit arrangement for output-impedance to the end of the inductance connectedto the corresponding screen-grid.

2. An amplifying circuit arrangement as claimed in claim 1, in which the screen-grid of each amplifying system is furnished with two separated supply leads, thescreen-grid being connected through one of these supply leads to the anode and through the other supply lead to the cathode.

3. An amplifying circuit arrangement for ultra-short waves including a push-pull circuit of two'amplifying systems each of which comprises at least one cathode, one control-grid, one

screen-grid and one anode and in which the cathodes of the two systems are interconnected through as short a lead as possible so as to provide negligible impedance, each screen-grid being connected for high frequencies to ,the corresponding cathode through an inductance which is so proportioned that the input-damping of the circuit is zero or negative, and the anode of each amplifying system being connected for high frequencies through the corresponding part of the output-impedance to an intermediate point on the inductance connected to the corresponding screen-grid.

4. An amplifying circuit arrangement as claimed in claim 3, in which the anode of each amplifying system is connected through the corresponding part of the output-impedance to such a tapping point 'of the inductance connected to the corresponding screen-grid that the inductance located between the screen-grid andthe tapping point has the value required for complete compensation of the distribution no1se. J

5. A circuit for the amplification of ultra-short waves comprising a push-pull tube provided with two electrode systems each of which has at least a cathode, a signal control grid, 9. screen grid and an anode, the cathodes being directly connected together within the tube, an input circuit connected to the signal control grids, an

output circuit connected to each anode, an invided with two electrode systems each of which has at least a cathode, a signal control grid, a,

screen grid and an anode, the cathodes being directly connected together within the tube, an input circuit connected to the signal control grids, an output circuit connected to each anode.

an inductance connected between each screen grid and the common cathode lead, and a connection from the low potential end of each output circuit to the screen grid end of the inductance connected to the corresponding screen grid, said screen grid inductances being of such value as to compensate for the damping of the input circuit.

'7. A circuit for the amplification of ultrashort waves comprising a push-pull tube provided with two electrode systems each of which has at least a cathode, a signal control grid, a screen grid and an anode, the cathodes being connected 'togetherby a path of minimum impedance, an input circuit connected to the signal control grids, an output circuit connected to each anode, an inductance connected between each screen grid and the common cathode lead, and a connection from the low potential end of each output circuit to an intermediate point on the inductance connected to the corresponding screen grid, said inductances being of such value that the common portions included in the screen grid and anode circuits compensate for the damping of the input circuit, and the remaining portions are adapted to increase the signal to noise ratio in the output circuits.

8. A circuit for the amplification of ultrashort waves comprising a push-pull tube provided with two electrode systems each of which has at least a cathode, a signal control grid, a screen grid and an anode, the cathodes being connected together by a path of minimum impedance, an input circuit connected to the signal control grids, an output circuit connected to each anode, two supply leads connected to each screen grid, an inductance connected between one supply lead of each screen grid and the common cathode lead, and a connection from the low potential end of each output circuit to the other screen grid supply lead, said inductances being of such value as to compensate for the damping of the input circuit. 

